1. Field of the Invention
This invention relates to an electron exit window assembly for a linear accelerator. In particular, this invention relates to a new material combination for the components used in such an assembly.
2. Prior Art
The U.S. Pat. No. 4,121,109 discloses an electron accelerator which is intended for use in medical radiotherapy. In this electron accelerator the accelerator tube is sealed by a vacuumtight beam exit window of special steel, transparent for electrons. In the beam direction beyond the beam exit window of the accelerator tube is a target which is made of a material of high atomic number, such as platinum, tantalum, gold or tungsten. And in the beam direction beyond the target is an electron absorber, in which any remaining electrons are filtered out of the X-ray cone. Finally, in the beam direction beyond the electron absorber is a collimator for masking out the active X-ray or beam cone, and a compensation body or filter through which the radiated intensity is equalized over the width of the beam cone.
In such an electron accelerator the electron beam exit window absorbs a certain part of the electron beam power to be supplied to the target and also limits the maximum electron beam power for thermal reasons. The electron absorption or capture rate should be kept low in order to improve the performance of the accelerator. Also the efficiency of the target should be increased in order to improve the generation of X-rays.